1979 GMC Pick-up Truck Differential Spool C1500 - GM 8.875 in.Rear - w/ 12 Bolt Cover - 30 Spline - Spartan Locker - Installs into standard open carrier case - Rear guaranteed to replace your current 1979 GMC Pick-up Truck Differential Spool C1500 - GM 8.875 in.Rear - w/ 12 Bolt Cover - 30 Spline - Spartan Locker - Installs into standard open carrier case - Rear. 1979 GMC Pick-up Truck Differential Spool comes new OEM 1979 GMC Pick-up Truck Differential Spool aftermarket new 1979 GMC Pick-up Truck Differential Spool of remanufactured 1979 GMC Pick-up Truck Differential Spool C1500 - GM 8.875 in.Rear - w/ 12 Bolt Cover - 30 Spline - Spartan Locker - Installs into standard open carrier case - Rear.